The present invention is in the field of an improved adhesive composition, use of said composition and products comprising said composition. The adhesive composition may be a one component and a two component adhesive, each component typically comprising various ingredients. The present adhesives are water-based dispersions.
The present invention is in the field of adhesives and for applying the adhesive to a first and/or second surface and then adhering the two surfaces. Prior art adhesives suffer from one or more disadvantages. Below an indication is given of various requirements of adhesives for a better understanding. It is noted that it is rather difficult to adapt characteristics of adhesives to specific requirements. It is intrinsically difficult to adapt properties of an adhesive, as improving a first characteristic may typically result in a deterioration of a second characteristic.
General properties of adhesives are open time (working time to make a bond, where the surface still retains sufficient tack, which can range from seconds for fast-setting adhesives to infinity for pressure-sensitive adhesives), set time (time to form a bond of acceptable strength), dry time, (initial) tack ((initial) degree of surface stickiness of the adhesive), applicability and adhesion to a diverse range of substrate surfaces, contactability, flexibility of an adhesive film, temperature stability, storage stability, viscosity, and surface energy (influences wetting of different kind of surfaces).
Adhesives often consist of one base material with various additives. For a two-component adhesive a first and second component, each component optionally comprising more than one constituent, are mixed shortly before applying, such as by a spray-gun. The first and second component can typically not be stored in a mixed form. Adhesives may relate to water based adhesives and to organic solvent based adhesives.
In manufacturing of larger objects, such as mattrasses and furniture, adhesives are often applied to fix parts of the large object together. Most adhesives are applied using either air-spray equipment or air-assisted spray equipment.
As mentioned above, a problem with many prior art aqueous adhesives is that they are not stable over time. For instance unexpectedly the plasticizer of the adhesive may partly or fully segregate from the adhesive composition, typically as a fluid like substance. As a result the adhesive can no longer be used, the equipment in use needs to be cleaned, production may need to be halted, etc.
A further problem is that for the dispersion component of an adhesive itself, either being the stabilized one component adhesive to be modified later before use, or the above first component of a two component system, the pH is also not stable. Typically the initial pH is in the order of 7-13.5. After addition (typically by intimately mixing) of further components, such as a plasticizer, the pH typically drops. Depending on the plasticizer used and the amount of plasticizer used the pH can easily drop 2.5-3.5 units (i.c. from about 12 to about 9). At a lower pH the adhesive composition is less stable. Such negatively effects the life time of the adhesive, the storage time, characteristics of the adhesive itself, such as open time and peel strength, and so on.
For specific applications a stable adhesive is required with a relatively low glass transition temperature Tg. Such may also be the case for adhesives that are used at relatively low temperatures.
Some background documents recite suitable preparation methods of benzoate esters. For instance, EP 1 415 978 A1 recites preparation methods of specific isododecyl benzoic esters. These ester can be used in non-aqueous, PVC compositions as a replacement of plasticizers that have insufficient cold flexibility at low viscosity and storage stability. The benzoate esters are incorporated in the PVC as a plasticizer in order to process the PVC further.
In an alternative hydroxy benzoic esters (which are different from the above benzoic esters) find use as solid plasticizers in non-aqueous heat-sensitive adhesive materials, further comprising a thermoplastic resin, typically acryl-based, which is obtainable by emulsion polymerization, and a tackifier (EP 2 397 531 A1). The document is concerned with a heat sensitive adhesive with improving tackiness to rough surface materials and blocking when using a thermal head for activation, and has good printer conveyance under high temperature and high humidity.
In an alternative approach to a dispersion of polychloroprene and the like water-soluble polysaccharides, such as celluloses, may be used (US 2006/157,196 A1), in combination with a high amount of a solubility reducing compound, i.e. to better dissolve the polysaccharide in water, and a polyimerizate, in order to obtain a high early tack. The solution can thus not be considered as a dispersion. A range of plasticers may be used.
In order to improve coalescing properties in latex based paint or as plasticizer in a dispersion of a synthetic elastomer (consisting of 60-75 wt. % polymer, 30-40 wt. % plasticer and 1-5 wt. % stabilizer), specific C10-C12 benzoic esters, and especially isododecyl esters are mentioned in U.S. Pat. No. 5,236,987 A. The document is in so far as plasticizers are concerned dedicated to PVC. In so far as paints are concerned high amounts of acrylate are present. For the present adhesives coalescence is discouraged.
It is therefore an object of the present invention to provide a water-based adhesive which overcomes one or more of the above disadvantages, without jeopardizing functionality and advantages.